Workers that can be exposed to flames, high temperatures, and/or electrical arcs and the like, need protective clothing and articles made from thermally resistant fabrics. Any increase in the effectiveness of these protective articles, or any increase in the comfort, durability, and dyeability of these articles while maintaining protection performance, is welcomed.
Polyoxadiazole polymers have unique properties and are useful in many fields, for example high performance fibers, such as flame retardant fibers. One method to improve flammability is to prepare sulfonated polyoxadiazole polymers. These methods have included the use of sulfonated monomers and post-sulfonation. Gomes et al. (US 20098/0318109, US2008/0193652, US2009/0203870) reacted hydrazine sulfate and aromatic dicarboxylic acids in phosphoric acid to form monosulfonated polyoxadiazole copolymers, and subsequently post-sulfonated the polymer. Another method is the use of oleum during polymerization to sulfonate the polymer as it is prepared. Lee et al. (U.S. Pat. No. 7,528,216 and U.S. Pat. No. 7,582,721) prepared random polyoxadiazole copolymers by reacting aromatic dicarboxylic acids with hydrazine sulfate in a limited amount of oleum, and prepared sulfonated random polyoxadiazole copolymers using sulfonated monomers (U.S. Pat. No. 7,528,217).
There is a need for an easy method to prepare polyoxadiazole polymers with a high degree of sulfonation that produce polymers with improved properties, such as flame retardancy, UV stability, and dyeability.